Remove unused FindDestinationIDCandidate API

- `FabricTable::FindDestinationIDCandidate` is declared, but used nowhere
  since the IPK refactor of #16737, and not implemented either. It is
  100% dead code.
- Remove stale `FindDestinationIDCandidate` API

src/credentials/FabricTable.h

@@ -392,9 +392,6 @@ class DLL_EXPORT FabricTable
  FabricInfo * FindFabricWithIndex(FabricIndex fabricIndex);
  FabricInfo * FindFabricWithCompressedId(CompressedFabricId fabricId);
 
- FabricIndex FindDestinationIDCandidate(const ByteSpan & destinationId, const ByteSpan & initiatorRandom,
- const ByteSpan * ipkList, size_t ipkListEntries);
-
  CHIP_ERROR Init(PersistentStorageDelegate * storage);
  CHIP_ERROR AddFabricDelegate(FabricTableDelegate * delegate);